Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FimH-Mech (The molecular mechanism of E. coli FimH pathogenicity)

Teaser

Escherichia coli bacteria, among other pathogenic bacteria, are responsible for a large variety of human diseases, including persistent urinary tract and intestinal infections. Their adhesion to the host cell wall is promoted by the binding of FimH located at the tip of the...

Summary

Escherichia coli bacteria, among other pathogenic bacteria, are responsible for a large variety of human diseases, including persistent urinary tract and intestinal infections. Their adhesion to the host cell wall is promoted by the binding of FimH located at the tip of the bacterial fimbriae to highly mannosylated cell surface receptors. Currently, antibiotics are still the standard treatment for E. coli infections; however, their long-term use promotes the development of microbial resistance, leading to recurrent infections and thus accounting for significant morbidity. As FimH-targeting drugs do not interfere with the bacterial metabolism and they have neither a bacteriostatic nor a bacteriolytic effect, they are unlikely to induce bacterial resistance. The reversible FimH-dependent attachment of E. coli is a necessity for the bacterial infection and colonization. The inhibition of this process could thus present an attractive alternative route to common antibiotic treatment of E. coli mediated diseases. To develop such inhibitors, the molecular recognition between FimH and its human receptors has to be better understood.
The FimH-Mech project intended to decipher the molecular mechanism that determines the pathogenicity of different E. coli strains, by the complex formation with one of its target receptors, namely the carcinoembryonic antigen-related cell adhesion molecule 6 or CEACAM6 in short. The biochemical nature and composition of the glycan attached to CEACAM6 was also investigated. Therefore, the binding affinities of glycans of growing complexity to FimH have been determined. To perform this study, a large variety of state-of-the-art computational and theoretical techniques have been applied, inspired by and complemented with experimental data measured in the host institute. Molecular modelling, molecular dynamics and free energy calculations have been combined to gain an understanding of the molecular action of bacterial adhesins and more specifically to decipher the glycan code for FimH lectin binding. The project’s results will allow the future development of more effective inhibitors and mark a milestone in the design of novel, promising non-antibiotic drugs to tackle harmful adhesive bacteria.

Work performed

Molecular modelling of the CEACAM6 receptor followed by glycosylation and molecular dynamics simulations has been performed. The resulting 3D-structures were docked to FimH, allowing to determine the interaction interface between the two proteins. In parallel, polymannosidic glycans and inhibitors have been generated and docked onto FimH, followed by molecular dynamics simulations. The energetics of the glycans/inhibitor binding was assessed in Molecular Mechanics – Poisson-Boltzmann Surface Area (MM-PBSA) calculations. The computed Gibbs free energies for binding were in line with experimentally determined affinities. Subsequently, these energies have been used to estimate the affinity for FimH of non-experimentally studied glycans, as well as of different inhibitors. These data allow to understand at the molecular level how FimH selects and recognizes its receptors and which residues are involved in the binding process between the FimH lectin and the receptor.
The results of this study will be published in a total of six articles, four that have already been published and two in preparation, and demonstrates how FimH selectively binds to well-defined mannosidic-linkages, as well how it recognizes its physiological glycoprotein receptor. Identified key residues as well as preferential binding modes will allow a better design of FimH-targeting molecules and will thus provide the basis for new non-antibiotic drugs for example against urinary tract infections.

Final results

The results of this study allowed to determine which glycan code FimH preferentially recognizes on its human receptors. These receptors might be differently expressed or glycosylated dependent on the different human conditions as it is the case in Crohn’s disease. This may explain why some patients have higher probability to have reoccurring E. coli infections than others. Furthermore, the data gained in this study will serve as the foundation for the future development of non-antibiotic drugs targeting FimH, in the case of different E. coli infections such as urinary tract infections, systemic infections or Crohn’s disease. As such my project could serve as model study for other pathogen-specific proteins that could be targeted for non-antibiotic drug development in other human diseases. On the long term, such a post-antibiotic approach to treat bacterial infections will have severe implications in the improvement of human health and might open a whole new branch in pharmaceutics.